The invention concerns a sealing arrangement with a seal for sealing a sealing surface between a first machine part having a seal accommodating structure, preferably a groove, and a second machine part, which comprises the sealing surface and can be moved relative to the first machine part, wherein the seal seals a high-pressure area between the machine parts from a low-pressure area.
Sealing arrangements of this type comprise a seal with a retaining element for positionally fixing the seal in the seal accommodating structure, and a sealing lip of elastomeric material, i.e. rubber-elastic material such as e.g. polyurethane or rubber, which is formed on the retaining element and has a sealing edge formed at a free end of the sealing lip for abutment on the sealing surface. The sealing lip has a high-pressure surface area bordering the high-pressure area, and a low-pressure surface area bordering the low-pressure area. The seals are normally designed as sealing rings and can be used both as rotary seals (radial shaft seal) and also as piston seals, i.e. a translational seal. When they are used as a rotary seal, one of the two machine parts is designed as a shaft that is rotatably supported inside a feed-through in the other machine part. When they are used as piston seals, the two machine parts move in an axial direction back and forth relative to each other. The seals can therefore be used as rod seals or piston seals for sealing purposes in hydraulic applications, pneumatic applications, e.g. pneumatic cylinders or valves and/or rotary seals, e.g. in high-pressure applications.
A seal of this type is normally inserted between two machine parts, which are moved in an axial direction relative to each other and/or in a rotary fashion, in a groove in a surface of one of the machine parts, wherein this surface is disposed opposite to a sealing surface formed by a surface of the second machine part. There is a sealing gap to be sealed between those surfaces. In the case of a sealing ring, the two surfaces are aligned concentrically with respect to one another. In this case, the groove is normally disposed in the corresponding surface of the outer machine part. The groove may, however, also be disposed in the inner machine part. The resilient sealing lip acts like a spring between the sealing edge and the retaining element such that the sealing edge abuts the sealing surface in a pretensioned state. The retaining element is dimensioned in such a fashion that it allows the seal to be preferably positionally fixed e.g. on the groove bottom.
When a seal of this type is used e.g. in a hydraulic cylinder, pneumatic cylinder or shaft seal such as e.g. a drive shaft of an engine, the seal is loaded by a pressurized medium on its high-pressure surface area during operation, i.e. by a fluid such as e.g. oil and/or air, which is located in the high-pressure area within the cylinder or the engine. In order to achieve the desired sealing effect, the seal is inserted in a pretensioned state into the seal accommodating structure.
Since the sealing lip is elastic, pressurization of the high-pressure surface area increases the pressure with which the sealing edge is pressed onto the sealing surface. In the static case, this increases the sealing force. In the dynamic case, the sealing edge might be deformed by the increased sealing force such that the sealing function of the sealing edge is reduced due to an unfavorable pressure distribution. The sealing lip may moreover be deformed in such a fashion that the sealing edge is lifted off from the sealing surface. The latter may happen, in particular, when the sealing lip is elastically and/or plastically deformed on the side of its low-pressure surface area, i.e. its surface area facing towards the outside, low-pressure area that usually borders the ambient air, and therefore fails to hold form.
These malfunctions of the seal during operation, e.g. of a pneumatic cylinder or engine, cause leakages in the high-pressure area and/or can cause a break in the lubricating film between the sealing surfaces due to undesired deformation in the sealing edge area, such that the surface of the sealing surfaces might be subjected to increased wear.
DE 32 12 476 C1 discloses a sealing arrangement with a seal with improved wear resistance. The seal has a supporting element disposed at a distance from the second machine part, the supporting element forming a support of the sealing lip on the low-pressure surface side. The support divides a high-pressure surface area of the sealing lip into a partial surface on the sealing edge side and a partial surface on the retaining element side. A center of rotation is thereby generated between the sealing edge and the supporting element and also between the supporting element and the retaining element, about which center of rotation the sealing lip can be pivoted when the shaft runs out with respect to the retaining element. This reduces wear of the sealing edge in case of shaft runouts. When the high-pressure surface area of the sealing lip is pressurized, the sealing lip is deflected about the center of rotation on the sealing edge side with respect to the retaining element, thereby pressing the sealing edge thereof against the sealing surface in dependence on the pressure that only acts on the partial surface on the sealing edge side.
DE 25 46 588 A1 discloses a sealing arrangement with a sealing ring comprising a sealing lip formed on a retaining element, the sealing lip being provided with a sealing edge at the free end thereof. The sealing ring is clamped between the sealing edge and the retaining element between a radially inner and a radially outer annular supporting element. The radially inner supporting element thereby forms a support of the sealing lip on the low-pressure surface side, the support substantially extending parallel to the sealing edge, wherein the support divides the high-pressure surface area of the sealing lip into a partial surface on the retaining element side and a partial surface on the sealing edge side. The low-pressure surface area of the sealing lip borders a free space delimited by the sealing lip and a machine part to be sealed between the support and the retaining element, into which free space the sealing lip can be pressed due to its deformation. The partial surface of the high-pressure surface area on the retaining element side is thereby larger than the partial surface on the sealing edge side. The sealing lip of this sealing arrangement can easily follow shaft runouts of a shaft to be sealed. In the pressure-activated state of the seal, the sealing lip is deformed into the free space, thereby axially shifting the sealing lip, which is reinforced by the support, with the sealing edge. When the pressure increases, the sealing edge is always pressed with increased force against the sealing surface of the shaft, thereby i.a. increasing wear of the sealing ring.
EP 1 760 371 A1 discloses a sealing arrangement with a radial shaft seal, in which a supporting element forms a support of the sealing lip on the low-pressure surface side, the sealing lip being arranged between the sealing edge and the retaining element. The support thereby divides a high-pressure surface area of the sealing lip into a partial surface on the retaining element side and a partial surface on the sealing edge side. Pressurization of the high-pressure surface area of the sealing lip of this seal may also load the sealing edge and cause great wear, in particular, in case of pressure peaks.
WO 2005/036033 A1 discloses a sealing arrangement, in which a small gap is formed between a supporting element forming a support of the sealing lip on the low-pressure side, and the sealing lip. The sealing edge could initially be relieved upon pressurization of its high-pressure surface area, thereby deforming the sealing lip into the free space. When the pressure further increases, the sealing lip abuts the supporting element with its full surface and the sealing edge is pressed against its associated sealing surface with an increasing force.
Comparable sealing arrangements are disclosed in DE 10 88 300 B, U.S. Pat. No. 2,743,950 A and DE 10 2008 017347 A1.
It is the underlying purpose of the invention to provide a sealing arrangement, which eliminates the disadvantages of prior art, in particular, reduces wear of the seal at the same time providing great reliability of the sealing function.
This object is achieved by the recitations of the independent claims. The dependent claims represent preferred embodiments of the invention.